It is important to control the cross-machine moisture profile on paper making machines such as tissue machines. Poor moisture profiles can result in a wide variety of operational problems, particularly in tissue converting operations.
A number of cross-directional moisture profile control devices are commercially available. These include steam boxes, electromagnetic induction devices, electric and gas infrared radiation devices, and profiling dampers.
The above-identified prior art devices are generally characterized by their inability to deliver more than a few per cent of the total drying energy of the dryer system. Consequently, none of the devices is truly effective insofar as correction of the moisture profile of a paper web is concerned. Also, many such prior art arrangements are characterized by their complexity and relatively high expense.
A patentability search directed to the present invention located the following U.S. Pat. Nos.: 2,268,988, issued Jan. 6, 1942, 3,163,502, issued Dec. 29, 1964, and 3,377,056, issued Apr. 9, 1968. None of the three located patents address the problem of moisture profile variations in a cross-machine direction.
U.S. Pat. No. 3,377,056 discloses a hood having a main housing and sub-housings on either side thereof. Cooling and heating components are located in the sides of the housing. Burners are provided in the walls of plenum chambers for heating the air supplied to the paper web positioned on a yankee dryer.
U.S. Pat. No. 2,268,988 discloses a manifold disposed around a drum. Burners are positioned around the circumference of the drum in order to heat ink which is positioned on paper transported around the outer surface of the drum.
U.S. Pat. No. 3,163,502 is directed to a removable hood for drying a web of material conveyed around cylinders. Heating ducts are provided in each of the hood sections. Gas heated by a fire tube may be substituted for the heater ducts. The ducts are essentially identical and each provides a passage at opposite ends communicating with an exhaust air chamber.